Net overseas migration (NOM) currently accounts for around half of Australia's population growth. The ABS estimates the level of NOM using data on incoming (i.e. arriving) and outgoing (i.e. departing) passenger movements at Australian air and sea ports.

Conceptually, NOM is the difference between permanent and long-term arrivals, and permanent and long-term departures. In practice, however, a number of adjustments are applied to overseas arrivals and departures data to produce estimates of NOM. These mainly comprise adjustments designed to reflect differences between stated travel intentions and actual travel behaviour, but also include adjustments to transform numbers of overseas movements into numbers of travellers. Until recently, adjustments used by the ABS to estimate NOM were referred to as 'category jumping adjustment'. They are now referred to more simply as 'migration adjustments'.